Antibacterial Activity of Liquid Facial Soap Formulated with Ethanol Extract of Syzygium myrtifolium Leaves against Cutibacterium acnes

Acne is a dermatological condition marked by follicular occlusion and inflammatory pustules, commonly attributed to colonization by Cutibacterium acnes. In response to the limitations and side effects of conventional therapies, research has increasingly focused on natural, plant-derived alternatives. Red pucuk leaves (Syzygium myrtifolium Walp.) have been reported to contain bioactive phytochemicals—such as flavonoids, saponins, and tannins—with established antibacterial properties. This study investigated the antibacterial efficacy of liquid facial soap formulations containing ethanol extracts of red pucuk leaves against C. acnes using a quasi-experimental design. A total of 24 experimental units were prepared, comprising six concentration groups (5%, 10%, 15%, 20%, 25%, and 30%) with four replications each. Additional comparative analysis included a positive control, a base formulation control, and an extract-only control to validate the observed antibacterial effects. Antibacterial activity was assessed via the Kirby-Bauer disc diffusion method, with mean inhibition zone diameters recorded as follows: 28.1 mm (5%), 25.9 mm (10%), 26.8 mm (15%), 27.0 mm (20%), and 30.1 mm for both 25% and 30% concentrations. According to interpretive criteria, all values fell within the category of "very strong" antibacterial activity. These results suggest that the red pucuk extract exerts a concentration-dependent inhibitory effect, peaking at 25–30%. Statistical analysis using simple linear regression revealed a significant positive correlation between extract concentration and inhibition zone diameter (p = 0.000, α < 0.05), indicating that the increase in extract concentration is scientifically associated with enhanced antibacterial activity against C. acnes.